Mass spectrometers for the investigation and for the detection of ions of specified mass numbers exhibit an ion source, an ion detection direction and an ion filter. The latter may be designed as a multipole, especially a quadrupole. The ions to be analyzed are directed through the multipole on their path to the detection device. Within the multipole, the ions experience a specified deflection. In the event of the use of a quadrupole, four elongate profiled surfaces which are directed toward one another are provided, which exhibit different electrical potentials. Surfaces which are hyperbolic in cross-section are particularly favorable for the design of the desired electric field between the pole surfaces. In some cases, surfaces which are circular in cross-section are employed.
For the purposes of specified practical applications, it is important to keep the dimensional tolerances of the finished ion filter as small as possible. The aim is to achieve tolerances of approximately one micrometer (1/1,000 mm ).
DE-OS 2,625,660 (corresponding to U.S. Pat. No. 4,158,771) discloses an ion filter which is designed as a quadrupole and which comprises, in total, two or four elongate segments. These are joined together in the region of mutually engaging projections and depressions. This gives, upon assembly, a certain degree of positional centering of the segments in relation to one another. The design of the projections and depressions is extremely difficult from the point of view of production technology, having regard to the required small tolerances. Thus, each part must be processed in the region of mutually parallel but remote surfaces and moreover mutually perpendicular surfaces. The best possible dimensional tolerances which result therefrom are not acceptable.